Process of producing trialkyl phosphites

ABSTRACT

A process of producing trialkyl phosphites by reacting phosphorus trichloride with an alcohol in an inert solvent wherein a tertiary amine is added as a hydrogen chloride acceptor along with anhydrous ammonia. The improvement comprises the steps of maintaining the pH at between 6 and 8 and a temperature between 40* and 80* C. for reacting a phosphorus trichloride with the alcohol. Moreover, the anhydrous ammonia is added after the initial reaction between the phosphorus trichloride and the alcohol so as to not interfere therewith.

United States Patent [72] inventor [2| Appl. No. [22] Filed [45 Patented[73] Assignee [54] PROCESS OF PRODUCING 'I'RIALKYL ruosmmzs 5 Claims, 1Drawing Hg.

52 us. 01 260/976 51 int. (I C07! 9/08 501 Field ol Search 260/976 [56]References Cited UNITED STATES PATENTS 3,057,904 10/1962 Reetzetal.

3,068,267 l2/l962 Becketal. 260/976 Primary Examiner-Charles B. ParkerAssistant Examiner-D. R. Phillips Attorneys Daniel C. Bloc lg Robert C.Sullivan Qqnald M.

ABSTRACT: A process of producing trialkyl phosphites by reactingphosphorus trichloride with an alcohol in an inert solvent wherein atertiary amine is added as a hydrogen chloride acceptor along withanhydrous ammonia. The improvement comprises the steps of maintainingthe pH at between 6 and 8 and a temperature between 40 and 80 C. forreacting a phosphorus trichloride with the alcohol. Moreover, theanhydrous ammonia is added after the initial reaction between thephosphorus tn'chloride and the alcohol so as to not interfere therewith.

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L.F HUM PH REY INVENTOR.

PROCESS OF PRODUCING TRIALKYL PHOSPI-II'I'FS BACKGROUND OF THE INVENTIONThe reaction of phosphorus trichloride and an alcohol in the presence ofa tertiary amine to produce a trialkyl phosphite is well known in theart, see for instance Kosolapoff, Organo- Phosphorus Compounds, page I84(John Wiley and Sons, (1958). There are certain disadvantages to thisprocess, however, particularly with the lower alkyl phosphites such astrimethyl phosphite where the amount of amine hydrochloride is largecompared with the amount of the product formed due to the high molecularweight of the tertiary amine hydrochloride. There is also a diflicultseparation problem under these circumstances with a relatively smallamount of liquid product and a large amount of solid byproducts.

Numerous attempts have been made to improve upon this basic process, asillustrated in US. Pat Nos. 2,843,616; 2,848,474; 2,859,238; 2,863,905and 2,678,940. In general, these patents illustrate the reaction betweenthe components by halting the attacks of the hydrogen chloride upon thetrialkyl phosphite. First and foremost, has been an attempt to keep thereaction mixture on the alkaline side or at a pH above 7.0. This hasbeen done by adding extensive tertiary amines as hydrogen chlorideacceptors or even adding ammonia directly to the charge to react withthe hydrogen chloride directly. This latter process has the disadvantageof requiring extremely careful and constant process control since slightexcess ammonia will react with the phosphorus trichloride to reduceyields by forming amidophosphites whereas slight deficiency of ammoniawill allow deleterious hydrochloride attacks of the alkyl phosphite asdiscussed above.

More recently, it has been proposed to produce a trialkyl phosphites byreacting phosphorus trichloride and alcohol at pHs as low as 2.5 withgood process control and excellent yields. This is brought about byadding less than a stoichiometric amount of certain tertiary amines tothe alcohol in an inert solvent and then while adding ICl continuouslyanhydrous ammonia is added. Thus, the hydrogen chloride first reactswith the tertiary amine to form an amine hydrochloride. This lattercompound is then continuously reacted with ammonia to regenerate theamine. By this means there is a continuous supply of tertiary aminepresent to react with the hydrogen chloride involved, yet the cost ofusing stoichiometric amounts of the amine as in the prior art isavoided. Likewise,

there is always amine hydrochloride present to react with ammonia so theprior art difficulty of forming amido phosphites is avoided. Thisprocedure is outlined and discussed in U.S. Pat. No. 3,068,267.

However, all the above processes lack the critical reaction conditionsin order to provide yields of above 80 percent BRIEF DESCRIPTION OF THEINVENTION It has been discovered that trialkyl phosphites can be made inyields above 80 percent by critically controlling the temperature ofreaction, the pH of the reaction medium at the feed of the component forreaction, and the position of injecting the anhydrous ammonia within thereaction medium. Thus, by controlling the reaction temperature ofbetween 40 and 80 C. and the pH of the reaction medium between 6 and 8and allowing the phosphorus trichloride and alcohol to react together asufficient length of time to provide initial reaction and then addinganhydrous ammonia, high' yields are obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration ofthe process embodying the present invention.

DETAILED DESCRIPTION OF THE INVENTION In practicing the presentinvention, a reactor chamber 1 provided with an agitator 2 havingagitator blades 3 attached thereto is charged with phosphorustrichloride and an alcohol in the presence of an inert solvent with atertiary amine as the hydrogen chloride acceptor. These materials arecharged into the reaction vessel 1 and 5 The temperature of the reactionvessel is maintained between 40 and C. Also, the pH of the reactionmedium is maintained at between 6 and 3 at the discharge of the infeedmaterials. This pH is measured by pH indicator 4. As is well known inthe art, the alcohol and phosphorus trichloride react together toprovide the trialkyl phosphites. As hydrogen chloride is evolved, thetertiary amines react therewith to form the amine hydrochloride. Thereaction medium is then pumped from reaction chamber 1 to a coolingchamber 9 via line 7 and pump 8. As the reaction medium flows down'thevessel 1, anhydrous ammonia is added at essentially the discharge end ofthe reaction chamber as indicated at 6. The function of the anhydrousammonia is to regenerate the amine that is initially added. The coolingchamber 9 is provided with the usual inlet 10 and exits 11 forcirculating a coolant therein. The reaction materials are dischargedinto line 12 and recycled back to the reaction chamber 1. In actualoperation, the product is removed at 13 with the mother liquor beingrecycled via line 12.

It is essential to the practice of the present invention that thetemperature within the reaction chamber 1 be maintained at between 40and 80 C., preferably up to about 60 C. Moreover, it is essential thatthe pH at the discharge of the infeed be maintained at between 6 and 8,along with the addition of the anhydrous ammonia at the discharge end ofthe reaction chamber. Thus, with a suitable flow rate provided withinthe recycling system, high yields of trialkyl phosphites can be producedwithout side reactions as is well known in the art.

Suitable tertiary amines would include pyridine, apicoline, quinoline,dimethyl aniline, and diethylaniline. The alcohol is selected forreaction with the phosphorus trichloride to provide the end productdesirable. Among the alcohols are the lower aliphatic alcohols such asmethyl alcohol, ethyl alcohol, butyl alcohol and the like. The amount oftertiary amine used may range between I and 20 percent of thatstoichiometric quantity necessary for acid acceptance.

By providing a recycling system as indicated above, the mother liquor iscontinuously replenished with the reacting components of phosphorustrichloride and a alcohol as necessary to provide optimum production. Byemploying this recycling system, yields well above 80 percent areachieved.

The following examples illustrate the process of this invention.

EXAMPLE A l-liter jacketed pipe reactor equipped with a high speedstirrer, thermometer and pH probe was charged with 1,l00 grams ofa'trimethyl phosphite reaction mixture. To this was continuously added16.1 gm./min. of phosphorus trichloride and l 1.2 gm./min of methylalcohol. These reactants were metered from calibrated dropping funnelsand were fed into the reaction mix through submerged tubes at a pointnear the top agitator blade. Simultaneously, 38.9 gm./min. of petroleumsolvent and 1.52 gm./min. of dimethyl aniline were added to the mix fromfeed reservoirs. The pH of the reaction mix was controlled between 6.0and 8.0 by feeding 5.9 gm./min. of gaseous ammonia into the reactor at apoint about 10 inches below the reactant feed point. The reactionmixture was pumped through an external heat exhanger. The reactiontemperature was maintained at 47 C. by circulating cold water in thereactor jacket and the shell side of the heat exchanger. A small amountof the recycle stream was removed to maintain a constant level in thereactor. After allowing a reasonable time to reach equilibrium, a sampleof the decanted liquor from the reaction mixture as analyzed to be atrimethyl phosphite yield of percent.

Example 11 In the same apparatus, as described in example 1, was charged1,100 grams of triethyl phosphite reaction slurry. To this wascontinuously added 17.8 grams of phosphorus trichloride and 19.6 gramsof ethyl alcohol. Simultaneously 51.9 grams of petroleum solvent and0.84 gm./min. of diethyl aniline were fed to the reaction mix. The pH ofthe reaction slurry was controlled between 6 and 8 by feeding ammonia ata rate of 8.4 gmJmin. The reaction temperature was maintained at 49 C.After the system was equilibrated, a sample of the decanted liquor fromthe reaction mixture was analyzed to be 92.5 percent yield of triethylphosphite.

EXAMPLE [1] An 8-gal1on jacketed reactor equipped with a high-speedturbine agitator, thermocouples and pH probe was charged with sufiicienttrimethyl phosphite reaction mixture to cover the agitator blades. Tothis was continuously added 191.0 gm./min. of phosphorus trichloride and129.5 gmjmin. of methanol. These reactant were metered into the reactionthrough dip tubes extending several inches below the surface of thereaction slurry. Simultaneously 390 gm./min. of petroleum solvent and14.0 gm./min. of diethyl aniline were fed through flowmeters into thereactor. The pH of the reaction mix was controlled between 6 and 8 bymetering 72.0 gm./min. of gaseous ammonia into the bottom of the reactorat a point 10 inches from the reactants feed point. The heat of thereaction was removed and the reaction temperature maintained at 54 C. bycirculation of cold water on the reaction jacket and pumping thereaction mixture through a water cooled heat exchanger. A small part ofthe recycle stream was continually removed to maintain a constant levelin the reactor. After operating for a time sufficient to reachequilibrium, a sample of the filtered reaction mixture was analyzed tobe a trimethyl phosphite yield of 9 l .4 percent.

EXAMPLE 1v 1n apparatus similar to that in example 111 was chargedsufficient triethyl phosphite reaction slurry to cover the agitatorblades. To this was continually fed 188 gmJmin. of phosphorustrichloride and 187.5 gm./min. of ethyl alcohol. Simultaneously 480gm./min. of petroleum solvent and 14.0 gm./min. of diethyl aniline werefed to the ,reaction mixture. The pH of this slurry was kept between 6and 8 by ammonia at a rate of 77.2 gin/min. The reaction temperature wasmaintained at 58 C. After the system was equilibrated, a sample of thefiltered reaction mix analyzed to be a triethyl phosphite yield of 93percent.

What is claimed is:

1. 1n the process of producing trialkyl phosphites by reactingphosphorus trichloride with a lower aliphatic alcohol in an inertsolvent using a tertiary amine as a hydrogen chloride acceptor andanhydrous ammonia to regenerate the tertiary amines, the improvementwhich comprises maintaining the temperature within the reaction mediumbetween 40 and C., maintaining the pH of the reaction medium between 6and 8 at the feed of the reactants into the reaction medium and addingthe anhydrous ammonia to the reaction medium after the initial reactionbetween the phosphorus trichloride and alcohol.

2. The process as set forth in claim 1, wherein the reaction between thephosphorus trichloride and alcohol is in a continuous recycling system.

3. The process of claim ll wherein the tertiary amine is dimethylaniline.

4. The process as set forth in claim ll wherein said tertiary amine ispyridine.

5. The process as set forth in claim 1 wherein said tertiary amine isdiethyl aniline.

2. The process as set forth in claim 1, wherein the reaction between thephosphorus trichloride and alcohol is in a continuous recycling system.3. The process of claim 1 wherein the tertiary amine is dimethylaniline.
 4. The process as set forth in claim 1 wherein said tertiaryamine is pyridine.
 5. The process as set forth in claim 1 wherein saidtertiary amine is diethyl aniline.